The photographic plate-making process for reproduction in the graphic arts includes steps of converting a photographic image having continuous gradation into a so-called dot image which represents light and shade of image by the size of dot areas, and combining the resulting dot image with characters and line original, thereby making a printing master.
In order to reproduce photographic line and dot images in a desirable condition, it is required that photographic materials for the photographic plate-making process have high contrast and high photographic density in order to have image areas distinguished clearly from nonimage areas, that is to say, to bear a so-called ultra-high contrasty photographic characteristic (particularly to have gamma of 10 or above).
In response to the expressed desire in this art to carry out a contact exposure step (a so-called contact work) under bright conditions using a light-sensitive material of relatively low photographic speed, photographic light-sensitive materials capable of being handled under conditions that can substantially be called bright conditions notwithstanding that silver halide is employed as the light-sensitive substance therein have been developed. The above-described desire can be fulfilled by employing a light-sensitive material which contains silver halide grains formed in the presence of an inorganic desensitizer such as a rhodium salt, an iridium salts, cupric chloride or so on, or a silver halide emulsion to which an organic desensitizer such as pinakryptol yellow, phenosafranine, or so on is added, whereby the sensitivity of the silver halide emulsion is extremely lowered (to less than conventional ones by a factor of from 10.sup.4 to 10.sup.5) so that the material may not have any substantial sensitivities to visible rays of wavelengths not shorter than 400 nm, and exposing the light-sensitive material by means of a printer equipped with a powerful light source which can emit ultraviolet rays in large quantities (e.g., an ultra-high pressure mercury lamp, a metal halide lamp, etc.). However, such a light source suffers from disadvantages that it consumes electricity in great quantity (e.g., 1 to 2 KW), and the price thereof is very high. Therefore, it has been desired to develop light-sensitive materials which enable the use of a more economical light source of an energy saving type.
On the other hand, for the purpose of achieving ultra-high contrasty characteristics, (particularly gamma of 10 or above) in the photographic printing plate-making process, it has been conventional to employ a method in which a so-called lithotype silver halide photographic material comprising silver chlorobromide the halide composition of which is 40 mol % or less bromide and the remainder chloride, is treated with a hydroquinone developer (a lith developer) in which the effective concentration of sulfite ion is very low (generally 0.1 mol/liter or less). However, the developer used in such a method is extremely unstable to air oxidation because of a low sulfite ion concentration therein.
Therefore, it has been required to overcome the instability in image formation according to such lithographic development, and further to provide an image-forming system which can ensure ultra-high contrasty photographic characteristics not withstanding development using a processing solution excellent in keeping stability. Under these circumstances, systems for forming ultra-high contrasty negative images having gamma of 10 or above, which consist in processing surface latent image type silver halide photographic material, in which particular acylhydrazine derivatives were incorporated, with a developer adjusted to a pH of from 10.5 to 12.3 and containing a sulfite preservative in a concentration of 0.15 mol/liter or more, thereby achieving excellent keeping stability, have been described in U.S. Pat. Nos. 4,166,742, 4,168,977, 4,221,857, 4,224,401, 4,243,739, 4,272,606, 4,311,781, and so on.
In such stable systems for image formation, ultra-high contrasty gradation is obtained by taking advantage of the electron injection reaction of hydrazine derivatives into silver halides. Accordingly, if a large amount of desensitizer were to be incorporated into silver halide grains and/or an emulsion layer of such a system, it would be expected that the contrast would be decreased.
Moreover, addition of a safelight dye to an emulsion layer for the purpose of lowering sensitivity to visible rays has been found to cause the loss of capabilities in controlling line width of characters and tone of dot images in the contact work, (which signify more specifically the abilities to make the width of the line image somewhat broader than that of characters of an original, and to enlarge dot areas of halftone image to some extent, compared with those of an original). In the contact work, not only is the ability to reproduce exactly the same line with and dot area as those of an original required, but also the capability of introducing modifications into an original with the intention of adding artistic expression to line and halftone images is required. Furthermore, the addition of a safelight dye has turned out in some cases to check the above-described contrast-increasing effect of hydrazine derivatives.